An investigation will continue of the mechanisms governing the operation of the lower esophageal sphincter. A new hypothesis, accounting for the operation of the smooth-muscle esophagus, will be tested in various ways: (1) certain electrophysiological characteristics of the muscle will be examined; (2) certain mechanical properties of the muscle will be described; (3) the nature of the synaptic transmission between the cryptic inhibitory nerves of the esophagus and the smooth muscle will be investigated.